Related
So I have a system that essentially enabled communication between two computers, and uses a WebRTC framework to achieve this:
"The Host": This is the control computer, and clients connect to this. They control the clients window.
"The Client": The is the user on the other end. They are having their window controlled by the server.
What I mean by control, is that the host can:
change CSS on the clients open window.
control the URL of an iframe on the clients open window
There are variations on these but essentially thats the amount of control there is.
When "the client" logs in, the host sends a web address to the client. This web address will then be displayed in an iframe, as such:
$('#iframe_id').attr("src", URL);
there is also the ability to send a new web address to the client, in the form of a message. The same code is used above in order to navigate to that URL.
The problem I am having is that on, roughly 1 in 4 computers the iframe doesn't actually load. It either displays a white screen, or it shows the little "page could not be displayed" icon:
I have been unable to reliably duplicate this bug
I have not seen a clear pattern between computers that can and cannot view the iframe content.
All clients are running google chrome, most on an apple powermac. The only semi-link I have made is that windows computers seem slightly more susceptible to it, but not in a way I can reproduce. Sometimes refreshing the page works...
Are there any known bugs that could possibly cause this to happen? I have read about iframe white flashes but I am confident it isn't that issue. I am confident it isn't a problem with jQuery loading because that produces issues before this and would be easy to spot.
Thanks so much.
Alex
edit: Ok so here is the code that is collecting data from the server. Upon inspection the data being received is correct.
conn.on('data', function(data) {
var data_array = JSON.parse(data);
console.log(data_array);
// initialisation
if(data_array.type=='init' && inititated === false) {
if(data_array.duration > 0) {
set_timeleft(data_array.duration); // how long is the exam? (minutes)
} else {
$('#connection_remainingtime').html('No limits');
}
$('#content_frame').attr("src", data_array.uri); // url to navigate to
//timestarted = data_array.start.replace(/ /g,''); // start time
ob = data_array.ob; // is it open book? Doesnt do anything really... why use it if it isnt open book?
snd = data_array.snd; // is sound allowed?
inititated = true;
}
}
It is definitele trying to make the iframe navigate somewhere as when the client launches the iframe changes - its trying to load something but failing.
EDIT: Update on this issue: It does actually work, just not with google forms. And again it isn't everybody's computers, it is only a few people. If they navigate elsewhere (http://www.bit-tech.net for example) then it works just fine.
** FURTHER UPDATE **: It seems on the ones that fail, there is an 'X-Frames-Origin' issue, in that its set the 'SAMEORIGIN'. I dont understand why some students would get this problem and some wouldn't... surely it depends upon the page you are navigating to, and if one person can get it all should be able to?
So the problem here was that the students were trying to load this behind a proxy server which has an issue with cookies. Although the site does not use cookies, the proxy does, and when the student had blocked "third party cookies" in their settings then the proxy was not allowing the site to load.
Simply allowed cookies and it worked :)
iframes are one of the last things to load in the DOM, so wrap your iframe dependent code in this:
document.getElementById('content_frame').onload = function() {...}
If that doesn't work then it's the document within the iframe. If you own the page inside the iframe then you have options. If not...setTimeout? Or window.onload...?
SNIPPET
conn.on('data', function(data) {
var data_array = JSON.parse(data);
console.log(data_array);
// initialisation
if (data_array.type == 'init' && inititated === false) {
if (data_array.duration > 0) {
set_timeleft(data_array.duration); // how long is the exam? (minutes)
} else {
$('#connection_remainingtime').html('No limits');
}
document.getElementById('content_frame').onload = function() {
$('#content_frame').attr("src", data_array.uri); // url to navigate to
//timestarted = data_array.start.replace(/ /g,''); // start time
ob = data_array.ob; // is it open book? Doesnt do anything really... why use it if it isnt open book?
snd = data_array.snd; // is sound allowed?
inititated = true;
}
}
}
One of our client is getting ""SCRIPT5: Access is denied" error when accessing web sites on Windows 8.1/IE11. Only one client is having this issue not all.
when we looked at the error message it turns ut it failed when tried to access
_global.localStorage
Client said its working fine if they add our site in "Trusted Site".
the problem we having is that none of our dev/test environments has this issue.we are running same version of OS and IE as client. so we are having bit difficulty trying to reproduce this issue.
sa mentioned here
Access Denied for localstorage in IE10
i have tried turn on/off DOMStorage/Enhance Protection Mode/Protection Mode but still no luck.
our best guess so far is there must be some setting/group policy which applied by Client's IT dept which causes this issue rather code issue as it works for all other clients.
so my question here is
which setting/group policy/domain setting i can check so that i can reproduce this error.
How can i fix the issue w/o making any code change as client has more than 1000 users so only changing the policy by IT dept is the only option here rather asking every user to add to "Trusted Site"
is there anything that i missed to check.
any help would be awesome.
I had the same issue and solved it in the next way:
let storage;
try {
storage = localStorage; // throws error if not supported by browser
} catch(e) { // caching this error and assigning fallback
let innerStorage = {};
storage = {
getItem: function(e) {
return innerStorage[e]
},
setItem: function(e, i) {
return innerStorage[e] = i
},
removeItem: function(e) {
delete innerStorage[e]
}
}
Best regards,
Aleh
I have created a custom URL protocol handler.
http://
mailto://
custom://
I have registered a WinForms application to respond accordingly. This all works great.
But I would like to be able to gracefully handle the case where the user doesn't have the custom URL protocol handler installed, yet.
In order to be able to do this I need to be able to detect the browser's registered protocol handlers, I would assume from JavaScript. But I have been unable to find a way to poll for the information. I am hoping to find a solution to this problem.
Thanks for any ideas you might be able to share.
This would be a very, very hacky way to do this... but would this work?
Put the link in as normal...
But attach an onclick handler to it, that sets a timer and adds an onblur handler for the window
(in theory) if the browser handles the link (application X) will load stealing the focus from the window...
If the onblur event fires, clear the timer...
Otherwise in 3-5seconds let your timeout fire... and notify the user "Hmm, looks like you don't have the Mega Uber Cool Application installed... would you like to install it now? (Ok) (Cancel)"
Far from bulletproof... but it might help?
There's no great cross-browser way to do this. In IE10+ on Win8+, a new msLaunchUri api enables you to launch a protocol, like so:
navigator.msLaunchUri('skype:123456',
function()
{
alert('success');
},
function()
{
alert('failed');
}
);
If the protocol is not installed, the failure callback will fire. Otherwise, the protocol will launch and the success callback will fire.
I discuss this topic a bit further here:
https://web.archive.org/web/20180308105244/https://blogs.msdn.microsoft.com/ieinternals/2011/07/13/understanding-protocols/
This topic is of recent (2021) interest; see https://github.com/fingerprintjs/external-protocol-flooding for discussion.
HTML5 defines Custom scheme and content handlers (to my knowledge Firefox is the only implementor so far), but unfortunately there is currently no way to check if a handler already exists—it has been proposed, but there was no follow-up. This seems like a critical feature to use custom handlers effectively and we as developers should bring attention to this issue in order to get it implemented.
There seems to be no straightforward way via javascript to detect the presence of an installed app that has registered a protocol handler.
In the iTunes model, Apple provides urls to their servers, which then provide pages that run some javascript:
http://ax.itunes.apple.com/detection/itmsCheck.js
So the iTunes installer apparently deploys plugins for the major browsers, whose presence can then be detected.
If your plugin is installed, then you can be reasonably sure that redirecting to your app-specific url will succeed.
What seams the most easy solution is to ask the user the first time.
Using a Javascript confirm dialog per example:
You need this software to be able to read this link. Did you install it ?
if yes: create a cookie to not ask next time; return false and the link applies
if false: window.location.href = '/downloadpage/'
If you have control of the program you're trying to run (the code), one way to see if the user was successful in running the application would be to:
Before trying to open the custom protocol, make an AJAX request to a server script that saves the user's intent in a database (for example, save the userid and what he wanted to do).
Try to open the program, and pass on the intent data.
Have the program make a request to the server to remove the database entry (using the intent data to find the correct row).
Make the javascript poll the server for a while to see if the database entry is gone. If the entry is gone, you'll know the user was successful in opening the application, otherwise the entry will remain (you can remove it later with cronjob).
I have not tried this method, just thought it.
I was able to finally get a cross-browser (Chrome 32, Firefox 27, IE 11, Safari 6) solution working with a combination of this and a super-simple Safari extension. Much of this solution has been mentioned in one way or another in this and this other question.
Here's the script:
function launchCustomProtocol(elem, url, callback) {
var iframe, myWindow, success = false;
if (Browser.name === "Internet Explorer") {
myWindow = window.open('', '', 'width=0,height=0');
myWindow.document.write("<iframe src='" + url + "'></iframe>");
setTimeout(function () {
try {
myWindow.location.href;
success = true;
} catch (ex) {
console.log(ex);
}
if (success) {
myWindow.setTimeout('window.close()', 100);
} else {
myWindow.close();
}
callback(success);
}, 100);
} else if (Browser.name === "Firefox") {
try {
iframe = $("<iframe />");
iframe.css({"display": "none"});
iframe.appendTo("body");
iframe[0].contentWindow.location.href = url;
success = true;
} catch (ex) {
success = false;
}
iframe.remove();
callback(success);
} else if (Browser.name === "Chrome") {
elem.css({"outline": 0});
elem.attr("tabindex", "1");
elem.focus();
elem.blur(function () {
success = true;
callback(true); // true
});
location.href = url;
setTimeout(function () {
elem.off('blur');
elem.removeAttr("tabindex");
if (!success) {
callback(false); // false
}
}, 1000);
} else if (Browser.name === "Safari") {
if (myappinstalledflag) {
location.href = url;
success = true;
} else {
success = false;
}
callback(success);
}
}
The Safari extension was easy to implement. It consisted of a single line of injection script:
myinject.js:
window.postMessage("myappinstalled", window.location.origin);
Then in the web page JavaScript, you need to first register the message event and set a flag if the message is received:
window.addEventListener('message', function (msg) {
if (msg.data === "myappinstalled") {
myappinstalledflag = true;
}
}, false);
This assumes the application which is associated with the custom protocol will manage the installation of the Safari extension.
In all cases, if the callback returns false, you know to inform the user that the application (i.e., it's custom protocol) is not installed.
You say you need to detect the browser's protocol handlers - do you really?
What if you did something like what happens when you download a file from sourceforge? Let's say you want to open myapp://something. Instead of simply creating a link to it, create a link to another HTML page accessed via HTTP. Then, on that page, say that you're attempting to open the application for them. If it doesn't work, they need to install your application, which they can do by clicking on the link you'll provide. If it does work, then you're all set.
This was a recommended approach for IE by Microsoft support
http://msdn.microsoft.com/en-us/library/ms537503%28VS.85%29.aspx#related_topics
"If you have some control over the binaries being installed on a user’s machine, checking the UA in script seems like a relevant approach:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\Post Platform
" -- By M$ support
Every web page has access to the userAgent string and if you drop a custom post platform value, detecting this in javascript using navigator.userAgent is quite simple.
Fortunately, other major browsers like Firefox and Chrome (barring Safari :( ), do not throw "page not found" errors when a link with a custom protocol is clicked and the protocol is not installed on the users machine. IE is very unforgiving here, any trick to click in a invisible frame or trap javascript errors does not work and ends up with ugly "webpage cannot be displayed" error. The trick we use in our case is to inform users with browser specific images that clicking on the custom protocol link will open an application. And if they do not find the app opening up, they can click on an "install" page. In terms of XD this wprks way better than the ActiveX approach for IE.
For FF and Chrome, just go ahead and launch the custom protocol without any detection. Let the user tell you what he sees.
For Safari, :( no answers yet
I'm trying to do something similar and I just discovered a trick that works with Firefox. If you combine it with the trick for IE you can have one that works on both main browsers (I'm not sure if it works in Safari and I know it doesn't work in Chrome)
if (navigator.appName=="Microsoft Internet Explorer" && document.getElementById("testprotocollink").protocolLong=="Unknown Protocol") {
alert("No handler registered");
} else {
try {
window.location = "custom://stuff";
} catch(err) {
if (err.toString().search("NS_ERROR_UNKNOWN_PROTOCOL") != -1) {
alert("No handler registered");
}
}
}
In order for this to work you also need to have a hidden link somewhere on the page, like this:
<a id="testprotocollink" href="custom://testprotocol" style="display: none;">testprotocollink</a>
It's a bit hacky but it works. The Firefox version unfortunately still pops up the default alert that comes up when you try to visit a link with an unknown protocol, but it will run your code after the alert is dismissed.
You can try something like this:
function OpenCustomLink(link) {
var w = window.open(link, 'xyz', 'status=0,toolbar=0,menubar=0,height=0,width=0,top=-10,left=-10');
if(w == null) {
//Work Fine
}
else {
w.close();
if (confirm('You Need a Custom Program. Do you want to install?')) {
window.location = 'SetupCustomProtocol.exe'; //URL for installer
}
}
}
This is not a trivial task; one option might be to use signed code, which you could leverage to access the registry and/or filesystem (please note that this is a very expensive option). There is also no unified API or specification for code signing, so you would be required to generate specific code for each target browser. A support nightmare.
Also, I know that Steam, the gaming content delivery system, doesn't seem to have this problem solved either.
Here's another hacky answer that would require (hopefully light) modification to your application to 'phone home' on launch.
User clicks link, which attempts to launch the application. A unique
identifier is put in the link, so that it's passed to the
application when it launches. Web app shows a spinner or something of that nature.
Web page then starts checking for a
'application phone home' event from an app with this same unique ID.
When launched, your application does an HTTP post to your web app
with the unique identifier, to indicate presence.
Either the web page sees that the application launched, eventually, or moves on with a 'please download' page.
This may seem like a no-brainer, but I can't find a way to do this that isn't considered a security issue (other than the obvious ways)...
So, I want to build an add-on for Firefox to use with my team. Basically it will be a status bar icon letting us know if the authentication cookie for our tools site has expired, so we can tell without losing any work currently in the browser.
At first I thought I could have the add-on check the cookie, but this seems to be a huge hassle for such a simple idea. Then it occurred to me...DUH...that I could just have the add on try to access the main page of our site. If it gets a "Access Denied" response, it can show the icon for "Not Logged In", but if it gets anything else, it can show "Signed In".
However, all attempts to do this with AJAX are proving to be almost as difficult as my cookie attempts.
Is there a simple way, with javascript preferably, but in XUL otherwise, to say
var url = "http://example.com";
var response = pingURL(url, "blah);
status = (response = "Welcome!") ? "Signed in" : "Not Signed In";
where "pingURL" would be the method of "going" to the url and getting the response?
function checkAccess(url, callback) {
var xhr = new XMLHttpRequest();
xhr.open("GET", url);
xhr.onreadystatechange = function () {
if (xhr.readyState == 4) {
if (xhr.status == 200) {
callback(true);
} else {
callback(false);
}
}
};
}
This should work... Just call with "checkAccess('http://example.com', function(ready){});" as an example where ready is a boolean value.
Exactly why do you consider cookies a huge hassle? That would undoubtedly be faster and probably simpler to implement. Reading cookies from chrome is simple and well-documented. Ask for help if you can't figure out how to parse the cookie.
I have created a custom URL protocol handler.
http://
mailto://
custom://
I have registered a WinForms application to respond accordingly. This all works great.
But I would like to be able to gracefully handle the case where the user doesn't have the custom URL protocol handler installed, yet.
In order to be able to do this I need to be able to detect the browser's registered protocol handlers, I would assume from JavaScript. But I have been unable to find a way to poll for the information. I am hoping to find a solution to this problem.
Thanks for any ideas you might be able to share.
This would be a very, very hacky way to do this... but would this work?
Put the link in as normal...
But attach an onclick handler to it, that sets a timer and adds an onblur handler for the window
(in theory) if the browser handles the link (application X) will load stealing the focus from the window...
If the onblur event fires, clear the timer...
Otherwise in 3-5seconds let your timeout fire... and notify the user "Hmm, looks like you don't have the Mega Uber Cool Application installed... would you like to install it now? (Ok) (Cancel)"
Far from bulletproof... but it might help?
There's no great cross-browser way to do this. In IE10+ on Win8+, a new msLaunchUri api enables you to launch a protocol, like so:
navigator.msLaunchUri('skype:123456',
function()
{
alert('success');
},
function()
{
alert('failed');
}
);
If the protocol is not installed, the failure callback will fire. Otherwise, the protocol will launch and the success callback will fire.
I discuss this topic a bit further here:
https://web.archive.org/web/20180308105244/https://blogs.msdn.microsoft.com/ieinternals/2011/07/13/understanding-protocols/
This topic is of recent (2021) interest; see https://github.com/fingerprintjs/external-protocol-flooding for discussion.
HTML5 defines Custom scheme and content handlers (to my knowledge Firefox is the only implementor so far), but unfortunately there is currently no way to check if a handler already exists—it has been proposed, but there was no follow-up. This seems like a critical feature to use custom handlers effectively and we as developers should bring attention to this issue in order to get it implemented.
There seems to be no straightforward way via javascript to detect the presence of an installed app that has registered a protocol handler.
In the iTunes model, Apple provides urls to their servers, which then provide pages that run some javascript:
http://ax.itunes.apple.com/detection/itmsCheck.js
So the iTunes installer apparently deploys plugins for the major browsers, whose presence can then be detected.
If your plugin is installed, then you can be reasonably sure that redirecting to your app-specific url will succeed.
What seams the most easy solution is to ask the user the first time.
Using a Javascript confirm dialog per example:
You need this software to be able to read this link. Did you install it ?
if yes: create a cookie to not ask next time; return false and the link applies
if false: window.location.href = '/downloadpage/'
If you have control of the program you're trying to run (the code), one way to see if the user was successful in running the application would be to:
Before trying to open the custom protocol, make an AJAX request to a server script that saves the user's intent in a database (for example, save the userid and what he wanted to do).
Try to open the program, and pass on the intent data.
Have the program make a request to the server to remove the database entry (using the intent data to find the correct row).
Make the javascript poll the server for a while to see if the database entry is gone. If the entry is gone, you'll know the user was successful in opening the application, otherwise the entry will remain (you can remove it later with cronjob).
I have not tried this method, just thought it.
I was able to finally get a cross-browser (Chrome 32, Firefox 27, IE 11, Safari 6) solution working with a combination of this and a super-simple Safari extension. Much of this solution has been mentioned in one way or another in this and this other question.
Here's the script:
function launchCustomProtocol(elem, url, callback) {
var iframe, myWindow, success = false;
if (Browser.name === "Internet Explorer") {
myWindow = window.open('', '', 'width=0,height=0');
myWindow.document.write("<iframe src='" + url + "'></iframe>");
setTimeout(function () {
try {
myWindow.location.href;
success = true;
} catch (ex) {
console.log(ex);
}
if (success) {
myWindow.setTimeout('window.close()', 100);
} else {
myWindow.close();
}
callback(success);
}, 100);
} else if (Browser.name === "Firefox") {
try {
iframe = $("<iframe />");
iframe.css({"display": "none"});
iframe.appendTo("body");
iframe[0].contentWindow.location.href = url;
success = true;
} catch (ex) {
success = false;
}
iframe.remove();
callback(success);
} else if (Browser.name === "Chrome") {
elem.css({"outline": 0});
elem.attr("tabindex", "1");
elem.focus();
elem.blur(function () {
success = true;
callback(true); // true
});
location.href = url;
setTimeout(function () {
elem.off('blur');
elem.removeAttr("tabindex");
if (!success) {
callback(false); // false
}
}, 1000);
} else if (Browser.name === "Safari") {
if (myappinstalledflag) {
location.href = url;
success = true;
} else {
success = false;
}
callback(success);
}
}
The Safari extension was easy to implement. It consisted of a single line of injection script:
myinject.js:
window.postMessage("myappinstalled", window.location.origin);
Then in the web page JavaScript, you need to first register the message event and set a flag if the message is received:
window.addEventListener('message', function (msg) {
if (msg.data === "myappinstalled") {
myappinstalledflag = true;
}
}, false);
This assumes the application which is associated with the custom protocol will manage the installation of the Safari extension.
In all cases, if the callback returns false, you know to inform the user that the application (i.e., it's custom protocol) is not installed.
You say you need to detect the browser's protocol handlers - do you really?
What if you did something like what happens when you download a file from sourceforge? Let's say you want to open myapp://something. Instead of simply creating a link to it, create a link to another HTML page accessed via HTTP. Then, on that page, say that you're attempting to open the application for them. If it doesn't work, they need to install your application, which they can do by clicking on the link you'll provide. If it does work, then you're all set.
This was a recommended approach for IE by Microsoft support
http://msdn.microsoft.com/en-us/library/ms537503%28VS.85%29.aspx#related_topics
"If you have some control over the binaries being installed on a user’s machine, checking the UA in script seems like a relevant approach:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\Post Platform
" -- By M$ support
Every web page has access to the userAgent string and if you drop a custom post platform value, detecting this in javascript using navigator.userAgent is quite simple.
Fortunately, other major browsers like Firefox and Chrome (barring Safari :( ), do not throw "page not found" errors when a link with a custom protocol is clicked and the protocol is not installed on the users machine. IE is very unforgiving here, any trick to click in a invisible frame or trap javascript errors does not work and ends up with ugly "webpage cannot be displayed" error. The trick we use in our case is to inform users with browser specific images that clicking on the custom protocol link will open an application. And if they do not find the app opening up, they can click on an "install" page. In terms of XD this wprks way better than the ActiveX approach for IE.
For FF and Chrome, just go ahead and launch the custom protocol without any detection. Let the user tell you what he sees.
For Safari, :( no answers yet
I'm trying to do something similar and I just discovered a trick that works with Firefox. If you combine it with the trick for IE you can have one that works on both main browsers (I'm not sure if it works in Safari and I know it doesn't work in Chrome)
if (navigator.appName=="Microsoft Internet Explorer" && document.getElementById("testprotocollink").protocolLong=="Unknown Protocol") {
alert("No handler registered");
} else {
try {
window.location = "custom://stuff";
} catch(err) {
if (err.toString().search("NS_ERROR_UNKNOWN_PROTOCOL") != -1) {
alert("No handler registered");
}
}
}
In order for this to work you also need to have a hidden link somewhere on the page, like this:
<a id="testprotocollink" href="custom://testprotocol" style="display: none;">testprotocollink</a>
It's a bit hacky but it works. The Firefox version unfortunately still pops up the default alert that comes up when you try to visit a link with an unknown protocol, but it will run your code after the alert is dismissed.
You can try something like this:
function OpenCustomLink(link) {
var w = window.open(link, 'xyz', 'status=0,toolbar=0,menubar=0,height=0,width=0,top=-10,left=-10');
if(w == null) {
//Work Fine
}
else {
w.close();
if (confirm('You Need a Custom Program. Do you want to install?')) {
window.location = 'SetupCustomProtocol.exe'; //URL for installer
}
}
}
This is not a trivial task; one option might be to use signed code, which you could leverage to access the registry and/or filesystem (please note that this is a very expensive option). There is also no unified API or specification for code signing, so you would be required to generate specific code for each target browser. A support nightmare.
Also, I know that Steam, the gaming content delivery system, doesn't seem to have this problem solved either.
Here's another hacky answer that would require (hopefully light) modification to your application to 'phone home' on launch.
User clicks link, which attempts to launch the application. A unique
identifier is put in the link, so that it's passed to the
application when it launches. Web app shows a spinner or something of that nature.
Web page then starts checking for a
'application phone home' event from an app with this same unique ID.
When launched, your application does an HTTP post to your web app
with the unique identifier, to indicate presence.
Either the web page sees that the application launched, eventually, or moves on with a 'please download' page.